Question about 1999 GMC Jimmy

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Heat stuck on high heat with no blower working

The heat is stuck on high no matter what the thermostat says. The blower will not go on either. Makes a funny noise in the dash every now and then.

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Check your fuse on the side of the dash, driver side. Look to make sure the fuse has not gone bad, and replace if the fuse to your HAVC has gone bad.
The other thing that can cause this issue is bad vacuum line to your HAVC system. On the drivers side by the corner where the windshield meets in the engine compartment, there is where your vacuum canister. Follow the vacuum lines and look for any damaged lines throughout your jimmy and replace any damage lines.
Poor vacuum will cause the issues your have described and the other thing also that has been found is the vacuum switch to your 4WD on the transfer case to go bad and leak transmission fluid in to your vacuum line causing the same issues you have described.
Start from the beginning and 1.check the fuse, 2, check the vacuum line. 3 check to make sure there is no transmission fluid throughout your vacuum lines and replace the vacuum switch on the transfer case if there is. ($15.00 part at Auto Zone or Napa)
Thank you for using fixya and good luck

Posted on Jun 03, 2010


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